Photoactive Compound Gradient Photoresist

ABSTRACT

A system and method for forming photoresists over semiconductor substrates is provided. An embodiment comprises a photoresist with a concentration gradient. The concentration gradient may be formed by using a series of dry film photoresists, wherein each separate dry film photoresist has a different concentration. The separate dry film photoresists may be formed separately and then placed onto the semiconductor substrate before being patterned. Once patterned, openings through the photoresist may have a tapered sidewall, allowing for a better coverage of the seed layer and a more uniform process to form conductive materials through the photoresist.

This application is a divisional of U.S. patent application Ser. No.13/192,113 entitled “Photoactive Compound Gradient Photoresist,” filedon Jul. 27, 2011, which application is incorporated herein by reference.

BACKGROUND

Generally, electrical contact can be made to wafers or dies withinpackages, such as within a package-on-package (POP), by first applying aphotoresist over the wafers or dies. The photoresist may then bepatterned in order to expose portions of the wafers or dies to whichcontact is desired to be made. The patterning may be performed byexposing the photoresist to a radiation such as light in order toactivate photoactive chemicals that may make up one component of thephotoresist. A positive developer or a negative developer may then beused to remove either the exposed photoresist (for a negativedevelopment) or to remove the non-exposed photoresist (for a positivedevelopment).

Once the photoresist has been developed and patterned, electricalconnections to the exposed wafers or dies may be formed by formingconductive material into the patterned photoresist such that anelectrical connection is made. The conductive material may be formed byfirst applying a seed layer over the photoresist and along the sidewallsof the patterned photoresist. The seed layer may then be utilized, forexample, in an electroplating process in order to plate the conductivematerial over and into the patterned photoresist, thereby providing thedesired electrical connection to the underlying wafer or die.

However, because seed layers are utilized to form the conductivematerial, a problem can arise if gaps or other issues regarding the stepcoverage of the seed layer occurs. These gaps can be especiallyprevalent along the sidewalls of the photoresist if sputtering isperformed to form the seed layer and the photoresist has a verticalsidewall. These gaps could, in turn, could cause gaps, uneven plating,or other problems to occur while the seed layer is used as an initiatorfor the subsequent plating of the conductive material.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a package-on-package with a first wafer and a firstdie in accordance with an embodiment;

FIG. 2 illustrates a first photoresist formed over the first wafer andthe first die in accordance with an embodiment;

FIG. 3 illustrates a method of forming a dry film resist in accordancewith an embodiment;

FIG. 4 illustrates a patterning of the first photoresist in accordancewith an embodiment;

FIG. 5 illustrates a seed layer formed over the first photoresist inaccordance with an embodiment;

FIG. 6 illustrates a second photoresist formed over the seed layer inaccordance with an embodiment; and

FIG. 7 illustrates a conductive material formed within the firstphotoresist in accordance with an embodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of embodiments are discussed in detail below. Itshould be appreciated, however, that the embodiments provides manyapplicable inventive concepts that can be embodied in a wide variety ofspecific contexts. The specific embodiments discussed are merelyillustrative of specific ways to make and use the embodiments, and donot limit the scope of the embodiments.

The embodiments will be described with respect to embodiments in aspecific context, namely a gradient photoresist for semiconductorprocessing. The embodiments may also be applied, however, to otherphotosensitive compounds.

With reference now to FIG. 1, there is shown a package-on-package (POP)system 100 with a first wafer 103 and a first die 105. In an embodiment,the first wafer 103 may be, e.g., a plurality of logic dies (notindividually illustrated in FIG. 1) and the first die 105 may be, e.g.,a memory die connected to work in conjunction with one of the individualdies on the first wafer 103. However, as one of ordinary skill in theart will recognize, the precise functions of the first wafer 103 and thefirst die 105 are not limited to these described embodiments, and thefirst wafer 103 and the first die 105 may alternatively have otherconfigurations such as a memory-on-memory stacked system. Thisconfiguration and any other suitable packaging configurations mayalternatively be utilized while still remaining within the scope of theembodiments.

The first wafer 103 may comprise a first substrate 107, first activelayers 109 on the first substrate 107, a first passivation layer 111,and first contacts 113 through the first passivation layer 111. Thefirst substrate 107 may comprise bulk silicon, doped or undoped, or anactive layer of a silicon-on-insulator (SOI) substrate. Generally, anSOI substrate comprises a layer of a semiconductor material such assilicon, germanium, silicon germanium, SOI, silicon germanium oninsulator (SGOI), or combinations thereof. Other substrates that may beused include multi-layered substrates, gradient substrates, or hybridorientation substrates.

The first active layers 109 may comprise active devices andmetallization layers (not individually shown in FIG. 1). The activedevices may comprise a wide variety of active devices such ascapacitors, resistors, inductors and the like in order to generate thedesired structural and functional requirements of the design on thefirst substrate 107. The active devices may be formed using any suitablemethods either within or else on the surface of the first substrate 107.

The metallization layers are formed over the first substrate 107 and theactive devices and are designed to connect the various active devices toform functional circuitry. While represented together with the activedevices in FIG. 1 as a single layer, the metallization layers are formedof alternating layers of dielectric and conductive material and may beformed through any suitable process (such as deposition, damascene, dualdamascene, etc.). In an embodiment there may be four layers ofmetallization separated from the first substrate 107 by at least oneinterlayer dielectric layer (ILD), but the precise number ofmetallization layers is dependent upon the design for the firstsubstrate 107.

The first passivation layer 111 may be formed on the first active layers109 in order to provide protection from physical and environmental harmthat exposure may cause. The first passivation layer 111 may be made ofone or more suitable dielectric materials such as silicon oxide, siliconnitride, low-k dielectrics such as carbon doped oxides, extremely low-kdielectrics such as porous carbon doped silicon dioxide, combinations ofthese, or the like. The first passivation layer 111 may be formedthrough a process such as chemical vapor deposition (CVD), although anysuitable process may be utilized, and may have a thickness between about0.5 μm and about 5 μm, such as about 9.25 KA.

The first contacts 113 may be formed through the first passivation layer111 in order to provide for electrical contact to the underlying firstactive layers 109. The first contacts 113 and may be formed of aluminum,although any suitable conductive material may alternatively be utilized.Further, the first contacts 113 may be formed using any suitableprocess, such as a damascene process, or else may be formed prior to theformation of the first passivation layer 111 through a deposition andmasking/etching process. Any suitable method for forming the firstcontacts 113 may alternatively be utilized.

The first die 105 may comprise a second substrate 117, second activelayers 119, a second passivation layer 121, and a second contact 123formed through the second passivation layer 121. In an embodiment, thesecond substrate 117 may be similar to the first substrate 107, thesecond active layers 119 may be similar to the first active layers 109,the second passivation layer 121 may be similar to the first passivationlayer 111, and the second contact 123 may be similar to the firstcontacts 113. However, as one of ordinary skill in the art willrecognize, while these structures may be similar to the structures inthe first wafer 103, this is not intended to limit the presentembodiments, as any other suitable structures may alternatively beformed on the first die 105 while still remaining within the scope ofthe embodiments. The first die 105 may be connected to the first wafer103 through, e.g., ball grid arrays (not shown).

FIG. 2 illustrates the formation of a first photoresist 201 over thefirst wafer 103 and the first die 105. The first photoresist 201 maycomprise a mixture of photoactive compounds (PACs) and a polymeric resindissolved into a solvent. The solvent may comprise any suitable solventsuch as, e.g., n-methylpyrrolidone (NMP), a glycol ether such as2-methoxyethyl ether (diglyme), ethylene glycol monom-ethyl ether,propylene glycol monomethyl ether; lactates such as ethyl lactate ormethyl lactate; proponiates such as methyl proponiate, ethyl proponiateand ethyl ethoxy proponiate; or a ketone such as methylethyl ketone,cyclohexanone and 2-heptanone, suitable combinations of these, and thelike.

The PACs may be photoactive components such as photoacid generators,photobase generators, or free-radical generator, or the like, and thePACs may be positive-acting or negative-acting. In an embodiment inwhich the PACs are a photoacid generator, the PAC may comprisehalogenated triazines, onium slats, sulfonated esters, halogeneratedsulfonyloxy dicarboximides, diazodisulfones, α-cyanooxyamine-sulfonates,imidesulfonates, ketodiazosulfones, sulfonyldiazoesters,1,2-di(arylsulfonyl)hydrazines, suitable combinations of these, and thelike.

In an embodiment in which the PACs are a free-radical generator, thePACs may comprise n-phenylglycine, aromatic ketones such asbenzophenone, N,N-tetramethyl-4,4′-diaminobenzophenone [Michler'sketone], N,N′-tetraethyl-4,4′-diaminobenzophenone,4-methoxy-4′-dimethylaminobenzo-phenone,3,3′-dimethyl-4-methoxybenzophenone,p,p′-bis(dimethylamino)benzo-phenone,p,p′-bis(diethylamino)-benzophenone, anthraquinone,2-ethylanthraquinone, naphthaquinone and phenanthraquinone, benzoinssuch as benzoin, benzoinmethylether, benzomethylether,benzoinisopropylether, benzoin-n-butylether, benzoin-phenylether,methylbenzoin and ethybenzoin, benzyl derivatives such as dibenzyl,benzyldiphenyldisulfide and benzyldimethylketal, acridine derivativessuch as 9-phenylacridine and 1,7-bis(9-acridinyl)heptane, thioxanthonessuch as 2-chlorothioxanthone, 2-methylthioxanthone,2,4-diethylthioxanthone, 2,4-dimethylthioxanthone and2-isopropylthioxanthone, acetophenones such as 1,1-dichloroacetophenone,p-t-butyldichloro-acetophenone, 2,2-diethoxyacetophenone,2,2-dimethoxy-2-phenylacetophenone, and2,2-dichloro-4-phenoxyacetophenone, 2,4,5-triarylimidazole dimers suchas 2-(o-chlorophenyl)-4,5-diphenylimidazole dimer,2-(o-chlorophenyl)-4,5-di-(m-methoxyphenyl imidazole dimer,2-(o-fluorophenyl)-4,5-diphenylimidazole dimer,2-(o-methoxyphenyl)-4,5-diphenylimidazole dimer,2-(p-methoxyphenyl)-4,5-diphenylimidazole dimer,2,4-di(p-methoxyphenyl)-5-phenylimidazole dimer,2-(2,4-dimethoxyphenyl)-4,5-diphenylimidazole dimer and2-(p-methylmercaptophenyl)-4,5-diphenylimidazole dimmer, suitablecombinations of these, or the like.

In an embodiment in which the PACs are a photobase generator, the PACsmay comprise quaternary ammonium dithiocarbamates, alpha aminoketones,oxime-urethane containing molecules such as dibenzophenoneoximehexamethylene diurethan, ammonium tetraorganylborate salts, andN-(2-nitrobenzyloxycarbonyl)cyclic amines, suitable combinations ofthese, or the like. However, as one of ordinary skill in the art willrecognize, the chemical compounds listed herein are merely intended asillustrated examples of the PACs and are not intended to limit thepresent embodiments to only those PACs specifically described. Anysuitable PAC may alternatively be utilized, and all such PACs are fullyintended to be included within the scope of the present embodiments.

The polymeric resin may comprise, for example, polymerized units thatmay include one or more ethylenically or acetylenically unsaturatedmonomers. Such monomers may include, but are not limited to,polynorbornenes, (meth)acrylic acid, (meth)acrylamides,alkyl(meth)acrylates, alkenyl(meth)acrylates, aromatic(meth)acrylates,vinyl aromatic monomers, nitrogen-containing compounds and theirthio-analogs, substituted ethylene monomers, cyclic olefins, substitutedcyclic olefins, suitable combinations of these, and the like.Additionally, the polymeric resin may comprise homopolymers orcopolymers.

The first photoresist 201 may also comprise other materials that may aidin the placement, exposure, development, and removal of the firstphotoresist 201. Such materials may include surfactants, actinic andcontrast dyes, cross-linking agents, anti-striation agents,plasticizers, speed enhancers, sensitizers, combinations of these, andthe like. These and any other additive are fully intended to be includedwithin the scope of the embodiments.

In an embodiment the PACs within the first photoresist 201 may have aconcentration gradient. This concentration gradient may have a highconcentration of PACs adjacent to the first wafer 103 and have a reducedconcentration at a point removed from the first wafer 103. In otherwords the concentration of PACs in the first photoresist 201 may getsmaller as the first photoresist 201 extends away from the first wafer103.

To achieve this concentration gradient of PACs, the first photoresist201 may be a dry film photoresist and may comprise a plurality ofindividual dry film photoresist layers, such as a first dry filmphotoresist layer 203, a second dry film photoresist layer 205, a thirddry film photoresist layer 207, and a fourth dry film photoresist layer209. In an embodiment, the first dry film photoresist layer 203, thesecond dry film photoresist layer 205, the third dry film photoresistlayer 207, and the fourth dry film photoresist layer 209 may each have adifferent concentration of PACs such that the percentage of PACs in thefirst photoresist 201 has a gradient and decreases from the first dryfilm photoresist layer 203 to the fourth dry film photoresist layer 209in a step pattern.

In a specific embodiment, the first dry film photoresist layer 203 mayhave a concentration of PACs (in the solvent along with the resin andother additives) sufficient to reach the desired target criticaldimension. For example, in an embodiment in which the target criticaldimension is 100 μm, the concentration of PACs may be, e.g., betweenabout 70% and about 100%, such as about 85%. This concentration in thefirst dry film photoresist layer 203 to reach the target dimension maybe viewed as having a concentration of 100% PACs in that there is a fullconcentration of PACs to reach the target critical dimension.

The second dry film photoresist layer 205 may have a reduced percentageof PACs such that the concentration of PACs in the second dry filmphotoresist layer 205 may be about 10% lower than the concentration ofPACs in the first dry film photoresist 203, or a concentration of about90% PACs (relative to the 100% concentration in the first dry filmphotoresist 203). The concentration gradient may continue by having thethird dry film photoresist layer 207 have a percentage of PACs (relativeto the concentration in the first dry film photoresist 203) of about 80%and the fourth dry film photoresist layer 209 have a percentage of PACs(relative to the concentration in the first dry film photoresist 203) ofabout 70%. However, the precise numbers presented here are presented asbeing illustrative only, and are not intended to limit the presentembodiments in any fashion. Any suitable concentration gradient of PACsmay be utilized within the first photoresist 201 while still remainingwithin the scope of the embodiments.

The concentration gradient may be formed in the first photoresist 201 byforming the first dry film photoresist layer 203, the second dry filmphotoresist layer 205, the third dry film photoresist layer 207, and thefourth dry film photoresist layer 209 as separate individual layersprior to their placement over the first wafer 103 and the first die 105.Each of these separate individual layers may be formed with a separate,individual concentration of PACs, such as the 90% concentration of PACsfor the second dry film photoresist layer 205 and the 80% concentrationof PACs for the third dry film photoresist layer 207. Once theindividual layers have been separately formed, the first dry filmphotoresist layer 203, the second dry film photoresist layer 205, thethird dry film photoresist layer 207, and the fourth dry filmphotoresist layer 209 may each be sequentially placed onto the firstwafer 103 and the first die 105 through a process such a laminating orcold rolling.

FIG. 3 illustrates a dry film system 300 and process by which the firstdry film photoresist layer 203, the second dry film photoresist layer205, the third dry film photoresist layer 207, and the fourth dry filmphotoresist layer 209, may be formed. Looking first generally at the dryfilm system 300, raw materials 305 for the first dry film photoresistlayer 203, the second dry film photoresist layer 205, the third dry filmphotoresist layer 207, and the fourth dry film photoresist layer 209 mayenter the dry film system 300 in a mixture room 301 and either used orstored in dissolution tanks 302. The raw materials 304 may comprise,e.g., the polymeric resin, the PACs, the solvent, etc., described abovewith respect to FIG. 2. The mixture room 301 may receive the rawmaterials 305 for a photoactive mixture and mix the raw materials 305in, e.g., a mixing tank 303 in order to achieve a mixture 309 with aconsistent composition of the desired components (described in detailfor each of the individual layers below).

Once the appropriate mixture 309 for a dry film photoresist (e.g., thesecond dry film photoresist layer 205) has been reached, the mixture 309may be passed through to a deforming room 308 and through a deformingtank 310 and a filter 312 before entering a coater room 311. The coaterroom 311 may apply the mixture 309 to a base film 313 in order toprovide support and maneuverability to the mixture 309. The base film313 may be, for example, a polyester film derived from polyethyleneterephthalate, although any other suitable material for the base film313 may alternatively be utilized. The base film 313 may be, e.g., 16μm, 19 μm, or 25 μm, although these numbers are meant to be exemplaryonly, and any suitable thickness may alternatively be utilized.

In the coater room 311 the mixture 309 may be applied to the base film313 using, e.g., a coating machine 315. The coating machine 315 may be,e.g., a reverse roll coater, gravure coater, rod coater, air doctorcoater, or other suitable coating machine, and may apply the mixture 309to the base film 313 to form a coated base film 317. The coated basefilm 317 may then exit the coater room 311 and enter a dryer 319, wherethe coated base film 317 may be dried at a temperature of between about80° C. and about 110° C., such as about 100° C., for a time of betweenabout 1 hr and about 2 hr, such as about 1.5 hr.

Once dried, the coated base film 317 may pass to a laminate room 321,where it may pass a defect detecting device 323 and a thickness device325 for quality control purposes. Once the coated base film 317 isdetermined to be acceptable, the coated base film 317 may be laminatedwith a cover film 327 to form a finished dry film resist 329. The coverfilm 327 may be, e.g., a polyester cover film with a thickness ofbetween about 15 mm and about 40 mm, such as about 20 mm. However, anysuitable material and thickness for the cover film 327 may alternativelybe utilized.

The finished dry film resist 329 may be stored in a first warehouse 331,sent to a slitting room 333 where the finished dry film resist 329 maybe cut to a desired shape and size using, e.g., a slit machine 335. Oncethe finished dry film resist 329 has been shaped, it may again be storedin a second warehouse 337 until it is ready for shipment 339 and foreventual usage.

While each of the first dry film photoresist layer 203, the second dryfilm photoresist layer 205, the third dry film photoresist layer 207,and the fourth dry film photoresist layer 209 may be formed using asimilar process, the raw materials and their respective concentrationsin the mixture 309 may be altered in order to form the first dry filmphotoresist layer 203, the second dry film photoresist layer 205, thethird dry film photoresist layer 207, and the fourth dry filmphotoresist layer 209. Looking first at the first dry film photoresistlayer 203, the first dry film photoresist layer 203 may be manufacturedsolely from PACs, with no other components such as the polymeric resinor solvents being added to the PACs within the mixture room 301, andonly PACs are coated onto the base film 313 and then covered by thecover film 327. Accordingly, the first dry film photoresist layer 203 is100% PACs.

The second dry film photoresist layer 205 may be formed by adding thepolymeric resin, solvent, and other additives at such an amount so thatthe mixture 309 used to form the second dry film photoresist layer 205has a concentration of about 90% PACs. Similarly, the third dry filmphotoresist layer 207 may be formed by adding into the mixture thepolymeric resin, solvent, and other additives at such an amount so thatthe mixture 309 used to form the third dry film photoresist layer 207has a concentration of about 80% PACs, and the fourth dry filmphotoresist layer 209 may be formed by adding into the mixture 309 thepolymeric resin, solvent, and other additives at such an amount so thatthe mixture 309 used to form the fourth dry film photoresist layer 209has a concentration of about 70% PACs. However, while these amounts arelisted as an illustrative example, one of ordinary skill in the art willrecognize that these are only examples, as any suitable concentrationsmay be utilized in order to form the desired concentration gradient.

Returning now to FIG. 2, once the first dry film photoresist layer 203,the second dry film photoresist layer 205, the third dry filmphotoresist layer 207, and the fourth dry film photoresist layer 209have been formed, each one of the first dry film photoresist layer 203,the second dry film photoresist layer 205, the third dry filmphotoresist layer 207, and the fourth dry film photoresist layer 209 maybe placed over the first wafer 103 and the first die 105. The placementof the first dry film photoresist layer 203, the second dry filmphotoresist layer 205, the third dry film photoresist layer 207, and thefourth dry film photoresist layer 209 may be performed sequentially by,e.g., laminating the first dry film photoresist layer 203, the seconddry film photoresist layer 205, the third dry film photoresist layer207, and the fourth dry film photoresist layer 209 onto the first wafer103 and the first die 105. However, any suitable method of sequentiallyplacing the first dry film photoresist layer 203, the second dry filmphotoresist layer 205, the third dry film photoresist layer 207, and thefourth dry film photoresist layer 209 may alternatively be utilized.

Looking at the lamination of the first dry film photoresist layer 203 asan illustrative example, the finished dry film resist 329 with theappropriate concentration of PACs (e.g., 100% PACs for the first dryfilm resist 329) may be put into a lamination machine (not shown). Thelamination machine may sequentially remove the base film from thefinished dry film resist 329 in order to expose the mixture 309, andthen contact the mixture 309 to the first wafer 103 and the first die105. Once the mixture 309 has bonded to the first wafer 103 and thefirst die 105, the lamination machine may then remove the cover film327, thereby leaving the mixture 309/first dry film photoresist layer203 on the first wafer 103 and the first die 105. The remaining seconddry film photoresist layer 205, the third dry film photoresist layer207, and the fourth dry film photoresist layer 209 may then similarly beplaced onto the first dry film photoresist layer 203 using a similarprocess.

By sequentially placing the first dry film photoresist layer 203, thesecond dry film photoresist layer 205, the third dry film photoresistlayer 207, and the fourth dry film photoresist layer 209 (with each onehaving a different concentration of PACs) onto the first wafer 103 andthe first die 105, the concentration gradient of PACs may be formedwithin the first photoresist 201. In the specific embodiment describedabove, this concentration gradient may begin with a 100% concentrationof PACs adjacent to the first wafer 103 (in the first dry filmphotoresist layer 203) and decreases in step concentrations as eachadditional layer is laminated onto the first wafer 103 and the first die105.

FIG. 4 illustrates that, once the first photoresist 201 with theconcentration gradient has been laminated over the first wafer 103 andthe first die 105, the first photoresist 201 may be patterned to formfirst openings 401 to the first wafer 103 and a second opening 403 tothe first die 105. The photoresist 203 may be patterned by exposing thephotoresist 203 to a form of radiation, such as light, in order toactivate the PACs within those portions of the photoresist 203 that wereexposed. The first photoresist 201 may then be exposed to a developer inorder to remove either those portions that were exposed (if a positivetone developer is used) or else those portions that were not exposed (ifa negative tone developer is used).

However, while photo-resists with a constant concentration of PACs maybe utilized to form vertical sidewalls, by having the concentrationgradient in the first photoresist 201 as described above with respect toFIG. 2, sidewalls 405 of the first openings 401 and the second opening403 may be tapered as the development process causes the regions withhigher concentrations of PACs to have a weaker coating than the regionswith lower concentrations of PACs. In other words, the greater theconcentration of PACs, the greater the cross-linking between thepolymers in the resin and the larger the opening will become. As such,in the embodiment described above with respect to the target criticaldimension being 100 μm, the first dry film photoresist 203 (with 100%PACs) may obtain an opening of about 100 μm, while the second dry filmphotoresist 205 (with 90% PACs) may obtain an opening of about 110 μm.These tapered sidewalls 405 allow for a more uniform deposition of asubsequently deposited seed layer 501 (discussed below with respect toFIG. 5). This more uniform deposition may reduce or eliminate gaps thatmay otherwise be formed during the deposition process.

FIG. 5 illustrates the formation of a seed layer 501 over the firstphotoresist 201 and along the sidewalls 405 and bottoms of the firstopenings 401 and the second opening 403. The seed layer 501 may be usedas an initiator for the further deposition of material (described belowwith respect to FIG. 7). The seed layer 501 may be deposited by PVD,CVD, sputtering, or the like, and may be formed of copper, nickel, gold,a titanium copper alloy, combinations of these, or the like, althoughother methods and materials may alternatively be used if desired.Additionally, the seed layer 501 may have a thickness of between about50 Å and about 1,000 Å.

FIG. 6 illustrates a second photoresist 601 formed over the seed layer501 once the seed layer 501 has been formed. The second photoresist 601may be formed of similar materials and in a similar fashion as the firstphotoresist 201, such as by laminating a series of dry film photoresistlayers with different concentrations of PACs onto the seed layer 501 inorder to obtain a concentration gradient of PACs within the secondphotoresist 601. Alternatively, the second photoresist 601 may be a wetor dry photoresist with a constant concentration of PACs throughout thesecond photoresist 601.

After the second photoresist 601 has been placed over the seed layer501, the second photoresist 601 may be patterned in order to coverportions of the seed layer 501 where a subsequent plating (describedfurther below with respect to FIG. 7) is not desired. To pattern thesecond photoresist 601, the second photoresist 601 may be exposed to,e.g., a radiation such as light in a desired pattern in order toactivate the PACs within the second photoresist 601. After beingexposed, the second photoresist may then be developed using, e.g., anegative-type or positive-type developer in order to expose regions ofthe seed layer 501 to which plating is desired.

After the second photoresist 601 has been patterned, conductive material701 may be formed within the first openings 401 and the second opening403 in order to provide electrical connection to both the first wafer103 and the first die 105. The conductive material 701 may comprisecopper, although other suitable materials such as aluminum, alloys,doped polysilicon, combinations thereof, and the like, may alternativelybe utilized. The conductive material 701 may be formed to a thickness ofbetween about 0.3 μm and about 0.6 μm, such as about 0.5 μm, and may beformed by electroplating copper onto the exposed portions of the seedlayer 501 (those portions not covered by the second photoresist 601),although any suitable alternative process for the formation of theconductive material 701 may alternatively be utilized.

By utilizing a photoresist with a concentration gradient of PACs, thesidewalls of subsequently formed openings through the photoresist may betapered. This tapering may help to prevent gaps and other coverageissues from arising during deposition of a seed layer. Without theseissues arising with the seed layer, a subsequently formed conductivematerial formed using the seed layer as an initiator may be formed withmore uniformity and consistency than may be otherwise possible.

In an embodiment a semiconductor device comprising a substrate and aphotoresist over the substrate is provided. The photoresist comprisesphotoactive compounds, the photoactive compounds having a concentrationgradient as the photoresist extends away from the substrate.

In another embodiment a semiconductor device comprising a firstsubstrate and a second substrate over the first substrate is provided. Aphotoresist is over the first substrate and the second substrate, thephotoresist having a first concentration of photoactive compoundsadjacent to the first substrate and a second concentration ofphotoactive compounds at a point removed from the first substrate, thesecond concentration of photoactive compounds being less than the firstconcentration of photoactive compounds. A first contact extends throughthe photoresist and in electrical connection with the first substrate,the first contact having a first tapered sidewall, and a second contactextending through the photoresist and in electrical connection with thesecond substrate, the second contact having a second tapered sidewall.

In another embodiment a method for forming a semiconductor device isprovided. The method comprises placing a first photoresist layer over asubstrate, the first photoresist layer having a first concentration ofphotoactive compounds, and placing a second photoresist layer over thefirst photoresist layer, the second photoresist layer having a secondconcentration of photoactive compounds, the second concentration ofphotoactive compounds being different from the first concentration ofphotoactive compounds. The first photoresist layer and the secondphotoresist layer are patterned to form a first opening through thefirst photoresist layer and the second photoresist layer.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. For example,the exact photoactive compounds utilized or the precise concentrationsused in order to form the concentration gradient may be adjusted whilestill remaining within the scope of the embodiments.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the embodiments, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to theembodiments. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. A semiconductor device comprising: a firstsubstrate and a second substrate over the first substrate; a photoresistover the first substrate and the second substrate, the photoresisthaving a first concentration of photoactive compounds adjacent to thefirst substrate and a second concentration of photoactive compounds at apoint removed from the first substrate, the second concentration ofphotoactive compounds being less than the first concentration ofphotoactive compounds; a first contact extending through the photoresistand in electrical connection with the first substrate, the first contacthaving a first tapered sidewall; and a second contact extending throughthe photoresist and in electrical connection with the second substrate,the second contact having a second tapered sidewall.
 2. Thesemiconductor device of claim 1, wherein the first substrate is asemiconductor substrate and the second substrate is a semiconductor die.3. The semiconductor device of claim 1, wherein there is a step profilebetween the first concentration and the second concentration.
 4. Thesemiconductor device of claim 1, wherein the photoresist is a dry filmphotoresist.
 5. The semiconductor device of claim 4, wherein the dryfilm photoresist further comprises: a first layer with a firstconcentration of photoactive compounds, the first layer being adjacentto the first substrate; and a second layer with a second concentrationof photoactive compounds, wherein the second layer is over the firstlayer and the second concentration is less than the first concentration.6. The semiconductor device of claim 5, further comprising: a thirdlayer with a third concentration of photoactive compounds, wherein thethird layer is over the second layer and the third concentration is lessthan the second concentration; and a fourth layer with a fourthconcentration of photoactive compounds, wherein the fourth layer is overthe third layer and the fourth concentration is less than the thirdconcentration.
 7. A method for forming a semiconductor device, themethod comprising: placing a first photoresist layer over a substrate,the first photoresist layer having a first concentration of photoactivecompounds; placing a second photoresist layer over the first photoresistlayer, the second photoresist layer having a second concentration ofphotoactive compounds, the second concentration of photoactive compoundsbeing different from the first concentration of photoactive compounds;and patterning the first photoresist layer and the second photoresistlayer to form a first opening through the first photoresist layer andthe second photoresist layer.
 8. The method of claim 7, wherein thesubstrate further comprises a first wafer and a first die, the first diebeing connected to the first wafer.
 9. The method of claim 7, furthercomprising: placing a third photoresist layer over the secondphotoresist layer, the third photoresist layer having a thirdconcentration of photoactive compounds, the third concentration ofphotoactive compounds being less than the second concentration ofphotoactive compounds.
 10. The method of claim 7, further comprising:forming the first photoresist layer as a first dry film photoresisthaving the first concentration of photoactive compounds prior to theplacing the first photoresist layer over the substrate; and forming thesecond photoresist layer as a second dry film photoresist having thesecond concentration of photoactive compounds prior to the placing thesecond photoresist layer over the first photoresist layer.
 11. Themethod of claim 7, wherein the second concentration of photoactivecompounds is less than the first concentration of photoactive compounds.12. The method of claim 7, further comprising: depositing a seed layerinto the first opening; and forming a conductive material in the firstopening.
 13. A semiconductor device comprising a first semiconductordie; a second semiconductor die over the first semiconductor die; afirst photoresist layer with a first concentration of photoactivecompounds; a second photoresist layer over the first photoresist layer,wherein the second photoresist layer has a second concentration ofphotoactive compounds, wherein the second concentration is differentfrom the first concentration; a first conductive material extendingthrough the first photoresist layer and the second photoresist layer tomake electrical contact with the first semiconductor die; and a secondconductive material extending through the first photoresist layer andthe second photoresist layer to make electrical contact with the secondsemiconductor die.
 14. The semiconductor device of claim 13, whereinthere is a step profile between the first concentration and the secondconcentration.
 15. The semiconductor device of claim 13, wherein thefirst photoresist layer is a dry film photoresist.
 16. The semiconductordevice of claim 13, further comprising a third photoresist layer with athird concentration of photoactive compounds, wherein the thirdphotoresist layer is over the second photoresist layer and the thirdconcentration is different than the second concentration
 17. Thesemiconductor device of claim 16, further comprising a fourthphotoresist layer with a fourth concentration of photoactive compounds,wherein the fourth photoresist layer is over the third photoresist layerand the fourth concentration is different than the third concentration.18. The semiconductor device of claim 13, wherein the first conductivematerial is tapered as it extends towards the first semiconductor die.19. The semiconductor device of claim 18, wherein the second conductivematerial is tapered as it extends towards the second semiconductor die.20. The semiconductor device of claim 13, wherein the first conductivematerial extends over the first photoresist layer.